Quarter-plate, 1849 daguerreotype of Isaac Morgan Mason (1831-1909), with note that was found in the case behind the image. The note reads: "Grandfather Isaac M. Mason at age of 18 C.P.M., Jr."
C.P.M. was Mason's grandson Charles Pressley Mason (1905-1999). I found a later photo of Isaac online and have confirmed 100% that this dag is of him.
At the age of 15 Isaac Mason began working as a second clerk on a ship on the Monogohela River. By the time this photo was taken at 18, he was first clerk on a Missouri River steam ship (this photo of him in uniform is probably commemorating the occasion), and in 1850, at only 19 years old, he became captain of his own ship. By the time he left the service in 1865, he had risen to Commander. For the next 16 years he was an agent for Northern Line Packet Company and eventually became one of St. Louis's most successful businessmen and politicians. In the 1870s he was elected St. Louis county and then city marshal; in 1880 and again in 1882 he was elected Sheriff of St. Louis. Mason was also a member of the Sons of the American Revolution, he was a mason, IOOF, Knights of Honor, St. Louis Legion of Honor, and Ancient Order of United Workmen. There is even a steamboat and elementary school named after him (Mason Elementary in St. Louis). If you search "Isaac M. Mason" in Google you'll find a lot of info on him.
The daguerreotype comes in a full, complete case with separated covers. Some tarnish, tarnish ring. The seals have dried up and fallen off inside of the case, but there is no damage to the plate. The only issue is the spot of tarnish next to his head, but this is cleanable by a conservator if it bugs you. The item in the lower-right isn't a scratch, it looks like a tarnished over painted gold object.
Boxed & signed Priority Mail.